Seismo Blog

Today in Earthquake History: Owens Valley 1872

Earthquakes in California, so it seems, occur mostly in the coastal regions of the
Golden State. Indeed, the San Andreas Fault and its sister fault lines are nowhere
more than a few dozen miles away from the Pacific shores, except for their
southernmost reaches around the Salton Sea in the Imperial Valley. And the
many temblors north of Cape Mendocino in far northern California also occur near
the coast. There the San Andreas Fault has ended and the plate boundary
becomes a subduction zone, where the Gorda plate dives beneath the North
American plate into Earth's mantle. So it may come as a surprise, that on this day
in 1872 California was shaken very hard by a strong quake with an epicenter
along the eastern flank of the Sierra Nevada. The magnitude of this "Owens
Valley Earthquake" was at least comparable, if not higher than that of the Great
San Francisco Earthquake 34 years later. Although no seismographs recorded the
1872 quake, modern calculations assign it a magnitude of 7.8 to 7.9. Taking the
uncertainties of such estimates into account, the strength of this quake may as
well have exceed an "8", which would make it the strongest temblor in California
in historical times.

The quake happened on March 26, 1872 at 2:30 in the morning. Its epicenter was
in view of Mt. Whitney, California's highest peak, near the mining camp of Lone
Pine. Except for a few other mining settlements, the Owens Valley was only
sparsely populated at this time. Nevertheless 27 inhabitants of Lone Pine were
killed – more than ten percent of its population. Of the 59 houses comprising that
settlement, 52 were destroyed (see Figure 1). The quake also left a profound
mark on the landscape, generating a fault scarp more than two meters tall, while
the ground also shifted about five meters to the right. That scarp was the result
of the shift of tectonic units during the rupture and could be followed – albeit not
as massive as in Lone Pine – for more than 40 miles to the north and to the south
of the epicenter. In fact, traces of this huge displacement can still be seen today
along the well-marked earthquake drive west of the current town of Lone Pine.
The quake was felt as far away as Sacramento and Los Angeles.

John Muir, the famous Scottish born naturalist, was awakened by the shaking in
his remote cabin in Yosemite Valley. He ran outside and in his typical poetic
exuberance yelled "A noble Earthquake!" As a keen observer of nature he
described the shaking "For a minute or two the shocks became more and more
violent--flashing horizontal thrusts mixed with a few twists and battering,
explosive, upheaving jolts". Nature fell silent for a few minutes after the shaking
had stopped. But then, Muir observed, "suddenly, out of the strange silence and
strange motion there came a tremendous roar. The Eagle Rock on the south wall,
about a half a mile up Yosemite Valley, gave way and I saw it falling in thousands
of the great boulders". The violent seismic shaking had set off one of the intensive
rock falls which occasionally happen in the famous granite valley.
How can the Earth shake so dramatically more than 200 miles away from the
nearest plate boundary further in the west? There are two factors to consider. The
Sierra Nevada mountains have been uplifting for more than a million years. The
strongest upwards push is on its eastern flank, which leads to an asymmetrically
tilted mountain range. While it takes hours to drive from the west until one
reaches the passes along the crest of the Sierra, the climb from the Owens Valley
in the east is much shorter, but considerably steeper. This uplift is still going on
and – as in 1872 –
can occasionally lead to strong earthquakes.

Another factor is that the Owens Valley is the westernmost extent of a geologic
province called "Basin and Range". It covers much of Nevada and some parts of
Utah and is characterized by dozens of parallel, north-south trending ranges
interspersed by long valleys extending along the same strike – the basins. This
topographic yin and yang is the result of a stretching of the Earth's crust in an
east-west direction. As the crust becomes thinner, whole blocks of rocks begin to
subside, creating the basins. This subsidence happens along faults at the foot of
the mountain ranges, where the basin side slips down relative to the mountain
side. In tectonics, this process is called normal faulting – a movement observed in
the Owens Valley quake.

As both the uplift of the Sierras and the crustal stretching in the Basin and Range
are still going on, the very big quake 147 years ago today was no singularity.
There is still significant seismicity in the Owens Valley, although no destructive
earthquakes have been recorded recently.
(hra164)